1. Field of the Invention
The present invention relates to an optical pickup apparatus for detecting a light spot reflected from a record track to read data recorded on the record track of a recording medium such as an optical disc and a card, and to a method of manufacturing such an optical pickup apparatus, and more particularly to an optical pickup apparatus for applying light spots to a plurality of tracks and reading data recorded on the tracks and to a method of manufacturing such an optical pickup apparatus.
The present invention also relates to an optical pickup apparatus to be used with a CD player or the like, a holder for holding a photodetector which is a component of the optical pickup apparatus, and a method of manufacturing such an optical pickup apparatus, and more particularly to an optical pickup apparatus, a holder, and a method of manufacturing the optical pickup apparatus, all of which facilitate the manufacture of the optical pickup apparatus.
2. Description of the Related Art
In an optical pickup apparatus for reading data recorded on a recording medium such as an optical disc and a card, a light beam is focussed on a track of the recording medium and the light beam reflected from the tack is detected with a photodetector.
Another type of an optical pickup apparatus has been proposed in which a plurality of light beams, e.g., seven light beams, are generated and corresponding seven spots are focussed on tracks of a recording medium to read data recorded on the tracks at the same time. With such a conventional optical pickup apparatus, light from a laser source is applied to a diffraction grating as light beam separation means to generate a plurality of light beams. These light beams are passed through a collimator lens and an objective lens and focussed on tracks of a recording medium in the form of light spots. Light spots reflected from the tracks are passed through the objective lens and collimator lens in the optical path opposite to the incoming optical path and through a focus adjusting lens, and are made incident upon photodiodes disposed, for example, along a direction perpendicular to the optical axis at a predetermined pitch corresponding to the reflected light spots. With the conventional optical pickup apparatus, each photodiode is directly mounted on a chassis at a predetermined photodiode mount position so as to make the reflected light beam passed through the focus adjusting lens become incident upon a corresponding photodiode.
In Japanese Laid-open Patent Application No. 8-221774, five light beams are generated and focussed upon tracks of a recording medium, and the light spots reflected from the tracks are detected. A single main spot is used for reading data recorded on the track, and other four spots are subsidiary spots which are used for servo tracking and are not used for reading data.
There are manufacture variations of laser oscillation frequencies and spaces between cells of lattice gratings. These variations affect a distribution pitch of reflected light beams along a direction perpendicular to an optical axis, so that the reflected light beam may not become incident upon the corresponding photodiode. A manufacture variation of ratios of focal lengths of collimator lenses to total focal lengths of collimator lenses and focus adjusting lenses may also affect the pitch between reflected light beams along a direction perpendicular to the optical axis. Specifically, with a conventional optical pickup apparatus, in order to compensate for the variation of pitches between reflected light beams along the direction perpendicular to the optical axis, the light reception area is made larger the farther the photodiode is positioned from the optical axis along the direction perpendicular to the optical axis. An increase in the light reception area of the photodiode results in poor frequency response characteristics (a lower high-cut frequency) of the photodiode and may degrade the apparatus performance.
In a conventional optical pickup apparatus used with a CD player or the like, a single light spot is used for reading data recorded on a CD. A single light beam from a light source is applied to a triangular prism to change its direction generally by a right angle, and passed through an objective lens to form a light spot on a track of CD. The reflected light beam is detected with a photodetector. The triangular prism is fixed to a chassis at a predetermined position by using predetermined positioning means such as a stopper.
Another optical pickup apparatus has been proposed in which a plurality of light beams, e.g., seven light beams, are generated and corresponding seven spots are focussed on tracks of a recording medium to read data recorded on the tracks at the same time.
In correctly focussing a plurality of spots on corresponding tracks of a recording medium and reliably detecting all the reflected spots and reading data, it is necessary for all the spots to enter an effective area of the objective lens projected upon respective tracks. In forming a plurality of spots on corresponding tracks, some spots may not enter the effective area of the objective lens projected upon respective tracks, because of work precision errors, dimension errors and mount errors of each component of the optical pickup apparatus. If a direction of a light beam is inclined relative to the track surface because of mount errors of an optical element, the focussing state of each spot may become inconsistent and unbalanced.
FIG. 28 shows a conventional holder 216 mounted on a base 212 of an optical pickup apparatus 210. The base 212 has a holder mount surface 214. The holder 216 of a block structure having a predetermined thickness has a bonding surface 240 and a non-bonding surface 242. The bonding surface 240 is adhered to the holder mount surface 214. A light reception unit receptacle 218 is formed in the central area of the non-bonding surface 218. A circular window 220 is formed on the bottom of the light reception unit 218 for passing a laser beam from a circular window 236 (FIG. 30) formed on the holder mount surface 214 side through this circular window 220. Pin fitting V-grooves 222 are formed through the whole thickness of the holder 216 on the right and left sides of the holder 216. A light reception unit 224 includes photodetectors or the like and has a shape and size conformal to the light reception unit receptacle 218 so that the former can be fitted in and mounted on the latter. A flexible print circuit (FPC) 226 is attached to the outer side surface of the light reception unit 224.
FIG. 29 illustrates a preliminary mount process for mounting the conventional holder 216 on the base 212. The horizontal and vertical directions are represented by x and y. The holder mount surface 214 is parallel to the x-y plane. The direction perpendicular to the x-direction is represented by z, and is perpendicular to the holder mount surface 214. An adjusting pin holder 254 has a pair of adjusting pins 256 extending along the z-direction and having tapered sharp ends. The adjusting pin holder 254 is movable along the x-, y- and z-directions. The adjusting pin holder 254 is moved first in the z-direction toward the non-bonding surface 242 of the holder 216 to partially insert the adjusting pins 256 into the pin adjusting V-grooves 222, and thereafter moved in the x- and y-directions to move the holder 216 in the x- and y-directions relative to the base 212 until a light reception plane of the light reception unit 224 reaches the optical axis of the laser beam supplied from the circular window 236 (FIG. 31) of the base 212. Next, instant adhesive 270 (FIG. 32) is dropped to two areas 266 on the upper side of the holder 216 to adhere the holder 216 to the holder mount surface 214 for the preliminary mount of the holder 216. Thereafter, the adjusting pin holder 254 is moved in the z-direction to be retracted from the base 212 so that the adjusting pins 256 are removed from the pin fitting V-grooves 222.
FIG. 30 shows another conventional holder 230 mounted on a base 212 of a conventional optical pickup apparatus 210. The main structure will be described. The holder 230 has a gate portion 232 which is floated over a holder mount surface 214. A light reception unit receptacle 218 is formed in the gate portion 232. A preliminary mount of the holder 230 on the base 212 is similar to that described with reference to FIG. 29. The tapered sharp ends of the adjusting pins 256 of the adjusting pin holder 254 are fitted into pin fitting V-grooves 222.
FIG. 31 shows another conventional holder 238 before it is mounted on a base 212 of an optical pickup apparatus 210. A circular hole 236 is formed in the base 212 on the holder mount surface 214 side, from which hole a laser beam is output to a light reception unit 224. The holder 238 has upper and lower projections extending to right and left sides thereof. These right and left projections are formed with idle holes 244 and pin holes 246 extending through the whole thickness of the holder 238. A pusher plate spring 248 is formed with recesses 250 and screw insertion holes 252 at positions corresponding to the pin holes 246 and idle holes 244 of the holder 238. A convex portion of the plate spring 248 is projected toward the bonding surface 240, and an apex of the convex portion abuts on the non-bonding surface 242 of the holder 216. The adjusting pin holder 254 is moved first to insert the adjusting pins 256 into the recesses 250 and partially insert the ends of the pins into the pin holes 246 of the holder, and then moved in the x- and y-directions. When the light reception plane of the light reception unit 224 reaches the optical axis of a laser beam supplied from the circular window 236, the holder 238 is stopped relative to the base 212. Thereafter, as shown in FIG. 29, the instant adhesive 270 is dropped to the two areas 266 to preliminary adhere the bonding surface 240 of the holder 238 to the holder mount surface 214. Lastly, fastening screws are inserted into the screw insertion holes 252 and idle holes 244 and threaded into screw holes 260 on both sides of the holder mount surface 214 to thereby fix the holder 238 to the holder mount surface 214. The size of the screw insertion hole 252 is set so that the holder 238 can be moved in the x- and y-directions relative to the holder mount surface 214 to determine the final mount positions by using the adjusting pins 256.
FIG. 32 illustrates an invasion of the instant adhesive into the pin fitting V-grooves 222 immediately after the holder 216 shown in FIG. 28 is preliminarily mounted. The tapered sharp ends of the adjusting pins 256 abut on the side edges of the pin fitting v-grooves 222 so that the pins are prevented from entering further the V-grooves and the tapered sharp ends are prevented from abutting on the holder mount surface 214.
Referring to FIG. 32, the instant adhesive 270 dropped to the two areas 266 (FIG. 29) flows into a gap between the holder mount surface 214 of the base 212 and the bonding surface 240 of the holder 240 and invades into the pin fitting V-grooves 222. The instant adhesive 270 then rises and invades into a space between the tapered sharp ends of the adjusting pins and the side walls of the holder 216 through capillarity. After the instant adhesive 270 is dropped to the two areas 266, the adjusting pins 256 is retracted from the holder 216 and pulled out of the pin fitting V-grooves 222. However, as shown in FIG. 32, the instant adhesive 270 invaded into the pin fitting V-grooves may be attached and adhered to the tapered sharp ends of the adjusting pins 256. In this case, when the adjusting pins 256 are pulled out of the pin fitting V-grooves 222, the holder 216 preliminarily mounted once on the holder mount surface 224 may be peeled off from the holder mount surface 214.